In recent years, it is a trend to produce semiconductor chips in reduced thickness, and it has been desired to decrease the thickness down to 50 to 100 μm or smaller. To decrease the thickness of the semiconductor chips, it is a generally accepted practice to grind the back surface of a wafer having a plurality of chips followed by dicing to form thin individual chips.
The following technologies have been known as methods of grinding the back surfaces.
First, a laminate structure comprising a wafer/an adhesive layer/a support material is fabricated by sticking a circuit surface of the wafer onto the support material via the adhesive layer. The wafer side of the laminate is ground to grind the back surface. After the back surface is ground, the support material and the adhesive layer are removed followed by dicing to divide the wafer into individual chips.
As the method of constituting the laminate comprising the wafer/adhesive layer/support material and as an exfoliating method therefor, there have been known methods of exfoliating and removing the adhesive layer and the support material, wherein a wafer is stuck onto an adhesive sheet obtained by providing, on, for example, a transparent resin support material, a pressure-sensitive adhesive layer that loses the adhering force upon being cured with ultraviolet rays and, after the back surface is ground, the adhesive sheet is irradiated with ultraviolet rays so that the adhesive sheet loses the adhering force (patent document JP-A-2002-373871, patent document JP-A-2003-209160 and patent document JP-A-2005-303068). There has further been known another method of exfoliating and removing a pressure-sensitive adhesive support material by sticking a wafer onto a pressure-sensitive adhesive substrate obtained by providing, on a transparent glass support material, a pressure-sensitive adhesive layer that foams and loses the adhering force upon the irradiation with ultraviolet rays, and by irradiating the adhesive layer with ultraviolet rays after the back surface has been ground (patent document JP-A-2005-197630). There has been known a further method of exfoliating and removing the support material by sticking a wafer, via a liquid adhesive layer, on a metallic, ceramic or glass support member having many through holes, solidifying the adhesive, grinding the back surface, and feeding a chemical solution that dissolves in the adhesive layer from the through holes (patent document JP-A-2005-191535). There has further been known a method wherein a wafer is stuck onto a glass support material having a special exfoliation layer on the surface thereof via a curable adhesive layer that cures by the external stimulation such as heat or ultraviolet rays, the back surface is ground in a state where the adhesive is cured and is held and, next, the exfoliation layer is exfoliated by using a laser to exfoliate and remove the support material (patent document JP-A-2004-64040).
There have further been disclosed so-called “pre-dicing methods” wherein grooves of a predetermined depth (also called half-cuts) are formed along the boundaries of the chips from the surface on the front surface side of the wafer (surface on where circuits are formed), and the back surface side of the wafer is ground to decrease the thickness of the chips, the grinding being continued so as to reach the bottoms of the grooves to divide the wafer into the individual chips (patent document JP-A-5-335411 and patent document JP-A-61-112345).
According to the above pre-dicing method as shown in FIG. 1, it is a generally accepted practice to fix a wafer 3 that is half cut along the boundaries of chips 4 to a support material 1 via an adhesive sheet 2, and to grind the back surface of the wafer 3. FIG. 1(a) is a schematic view of before and after grinding the chips of a small aspect ratio of when the circuit surface on the wafer is not so much rugged, half-cut portions are shallow, and the plane size (XY) of the chip is larger than the chip thickness (Z). In this case, the chips are stably fixed onto the wafer 3 and a favorable result of grinding is obtained. In recent years, however, there have been produced more chips having large ruggedness on the wafer circuit surface and more chips having large aspect ratios. FIG. 1(b) is a schematic view of before and after the grinding of when there are included chips of a large aspect ratio. When the back surface of the wafer 3 is to be ground, it becomes difficult to hold the chips 4 of a decreased thickness by using an adhesive sheet 2 and, hence, to smoothly grind the back surface. While grinding the back surface, further, there occur such problems as chip jumping or contact of the neighboring chips, causing the chips to be damaged.